Effect of Dietary Geranylgeraniol and Green Tea Polyphenols on Glucose Homeostasis, Bone Turnover Biomarkers, and Bone Microstructure in Obese Mice.

Previously, we demonstrated that the administration of either geranylgeraniol (GGOH) or green tea polyphenols (GTP) improved bone health. This study examined the combined effects of GGOH and GTP on glucose homeostasis in addition to bone remodeling in obese mice. We hypothesized that GGOH and GTP would have an additive or synergistic effect on improving glucose homeostasis and bone remodeling possibly in part via suppression of proinflammatory cytokines. Forty-eight male C57BL/6J mice were assigned to a high-fat diet (control), HFD + 400 mg GGOH/kg diet (GG), HFD + 0.5% GTP water (TP), or HFD + GGOH + GTP (GGTP) diet for 14 weeks. Results demonstrated that GTP supplementation improved glucose tolerance in obese mice. Neither GGOH nor GTP affected pancreas insulin or bone formation procollagen type I intact N-terminal, bone volume at the lumbar vertebrae, or bone parameters at the trabecular bone and cortical bone of the femur. There was an interactive effect for serum bone resorption collagen type 1 cross-linked C-telopeptide concentrations, resulting in no-GGOH and no-GTP groups having the highest values. GGOH increased trabecular number and decreased trabecular separation at the lumbar vertebrae. GTP increased trabecular thickness at lumbar vertebrae. The GG group produced the greatest connectivity density and the lowest structure model index. Only GTP, not GGOH, decreased adipokines concentrations (resistin, leptin, monocyte chemoattractant protein-1, and interleukin-6). In an obese male mouse model, individual GGOH and GTP supplementation improved glucose homeostasis, serum CTX, and trabecular microstructure of LV-4. However, the combined GGOH and GTP supplementation compromises such osteoprotective effects on serum CTX and trabecular bone of obese mice.

Deficiency of PPARγ in Bone Marrow Stromal Cells Does not Prevent High-Fat Diet-Induced Bone Deterioration in Mice.

BACKGROUND: Bone marrow osteoblasts and adipocytes are derived from a common mesenchymal stem cell and have a reciprocal relationship. Peroxisome proliferator-activated receptor gamma (PPARγ), a regulator for adipocyte differentiation, may be a potential target for reducing obesity and increasing bone mass. OBJECTIVES: This study tested the hypothesis that bone-specific Pparg conditional knockout (cKO), via deletion of Pparg from bone marrow stromal cells (BMSC) using Osterix 1 (Osx1)-Cre, would prevent high-fat (HF) diet-induced bone deterioration in mice. METHODS: PPARγ cKO (PPARγfl/fl: Osx1-Cre) and floxed littermate control (PPARγfl/fl Osx1-Cre- ) mice that were 6 weeks old were randomly assigned to 4 groups (n = 12/group, 6 male and 6 female) and fed ad libitum with either a normal-fat (NF) purified diet (3.85 kcal/g; 10% energy as fat) or an HF diet (4.73 kcal/g; 45% energy as fat) for 6 mo. Bone structure, body composition, and serum bone-related cytokines were measured. Data were analyzed by 2-way ANOVA with Tukey post hoc comparison. RESULTS: The HF diet decreased the tibial and lumbar vertebrae trabecular bone volume/total volume (BV/TV) by 28% and 18%, respectively, compared to the NF diet (P < 0.01). PPARγ cKO mice had 23% lower body fat mass and 9% lower lean mass than control mice. PPARγ cKO mice had 41% greater tibial trabecular BV/TV compared to control mice. None of trabecular bone parameters at the second lumbar vertebra were affected by genotype. PPARγ cKO mice had decreased cortical thickness compared to control mice. PPARγ cKO mice had a 14% lower (P < 0.01) serum concentration of leptin and a 35% higher (P < 0.05) concentration of osteocalcin compared with control mice. CONCLUSIONS: These data indicate that PPARγ has site-specific impacts on bone structures in mice and that knockout PPARγ in BMSC increased bone mass (BV/TV) in the tibia but not the lumbar vertebrae. PPARγ disruption in BMSC did not prevent HF diet-induced bone deterioration in mice.

Increasing Vegetable Intake Decreases Urinary Acidity and Bone Resorption Marker in Overweight and Obese Adults: An 8-Week Randomized Controlled Trial.

BACKGROUND: Controlled intervention trials are needed to confirm a positive association from epidemiological studies between vegetable consumption and bone health. OBJECTIVE: We investigated whether providing vegetables at the Dietary Guidelines for Americans (DGA) recommended amount affects excretion of acid and calcium in urine and bone turnover markers in serum in adults with low vegetable intake. METHODS: In total, 102 adults (19 males and 83 females, age 18-65 y, BMI ≥25 kg/m2) consuming ≤1 serving of vegetables (128 g raw leafy or 64 g cooked vegetables) per d were recruited in a 2-arm, parallel, randomized, controlled, and community-based 8-wk feeding intervention trial. The 2 arms included a vegetable intervention (VI) during which participants received extra vegetables (∼270 g/d) and an attention control (CON) group that conducted only the testing visits. Measurements included nutrient intake, plasma carotenoids, and bone-related markers in serum and urine. Differences between CON and VI at week 8 were tested using the ANCOVA with baseline values as a covariate. RESULTS: Compared with CON, carotenoid intake (mean ± SD) was higher (6.4 ± 3.4 compared with 2.0 ± 1.2 mg/d) (P < 0.01) and dietary potential renal acid load was lower (20 ± 13 compared with 3.4 ± 14 mEq/d) (P < 0.01) in VI. Compared with CON at week 8, urine titratable acid and Mg were 24 and 26% lower, respectively, while urine pH was 3% greater (P < 0.05) and serum C-terminal telopeptide of type I collagen (CTX) was 19% lower in VI. There were no group differences in serum concentrations of propeptide of type 1 procollagen and tartrate-resistant acid phosphatase or urinary excretion of deoxypyridinoline and CTX. CONCLUSIONS: Consumption of vegetables at the DGA-recommended amount by adults with low vegetable intake potentially benefits bone health. This trial was registered at clinicaltrials.gov as NCT02585102.

Increasing Dietary Fish Oil Reduces Adiposity and Mitigates Bone Deterioration in Growing C57BL/6 Mice Fed a High-Fat Diet.

BACKGROUND: Intake of total fat is linked to obesity and inversely associated with bone density in humans. Epidemiologic and animal studies show that long-chain n-3 (ω-3) PUFAs supplied as fish oil (FO) are beneficial to skeletal health. OBJECTIVE: This study tested the hypothesis that increasing dietary FO would decrease adiposity and improve bone-related outcomes in growing obese mice. METHODS: Male C57BL/6 mice at 6 wk old were assigned to 6 treatment groups and fed either a normal-fat diet (3.85 kcal/g and 10% energy as fat) or a high-fat diet (HF; 4.73 kcal/g and 45% energy as fat) containing either 0%, 3%, or 9% energy as FO (0FO, 3FO, and 9FO, respectively) ad libitum for 6 mo. Bone structure, body composition, and serum bone-related cytokines were measured. RESULTS: The HF diet increased the expression of the adipose tissue tumor necrosis factor α (Tnfa) and serum concentrations of leptin and tartrate-resistant acid phosphatase (TRAP), and decreased serum concentrations of osteocalcin and bone-specific alkaline phosphatase (P < 0.05). FO decreased fat mass (P < 0.05), serum TRAP (P < 0.05), and adipose tissue Tnfa expression (P < 0.01). Bone content of long-chain n-3 PUFAs was increased and n-6 PUFAs were decreased with the elevation in dietary FO content (P < 0.01). Compared with mice fed 9FO, animals fed 3FO had higher femoral bone volume/total volume (25%), trabecular number (23%), connectivity density (82%), and bone mass of second lumbar vertebrae (12%) and lower femoral trabecular separation (-19%). Mice fed the 3FO HF diet had 42% higher bone mass than those fed the 0FO HF diet. CONCLUSIONS: These data indicate increasing dietary FO ≤3% energy can decrease adiposity and mitigate HF diet-induced bone deterioration in growing C57BL/6 mice possibly by reducing inflammation and bone resorption. FO at 9% diet energy had no further beneficial effects on bone of obese mice.

Decreasing the Ratio of Dietary Linoleic to α-Linolenic Acid from 10 to 4 by Changing Only the Former Does Not Prevent Adiposity or Bone Deterioration in Obese Mice.

BACKGROUND: Linoleic acid (LA; 18:2n-6) has been considered to promote low-grade chronic inflammation and adiposity. Studies show adiposity and inflammation are inversely associated with bone mass. OBJECTIVES: This study tested the hypothesis that decreasing the dietary ratio of LA to α-linolenic acid (ALA, 18:3n-3), while keeping ALA constant, mitigates high-fat diet (HF)-induced adiposity and bone loss. METHODS: Male C57BL/6 mice at 6 wk old were assigned to 4 treatment groups and fed 1 of the following diets ad libitum for 6 mo: a normal-fat diet (NF; 3.85 kcal/g and 10% energy as fat) with the ratio of the PUFAs LA to ALA at 6; or HFs (4.73 kcal/g and 45% energy as fat) with the ratio of LA to ALA at 10:1, 7:1, or 4:1, respectively. ALA content in the diets was kept the same for all groups at 1% energy. Bone structure, body composition, bone-related cytokines in serum, and gene expression in bone were measured. Data were analyzed using 1-factor ANOVA. RESULTS: Compared with those fed the NF, mice fed the HFs had 19.6% higher fat mass (P < 0.01) and 13.5% higher concentration of serum tartrate-resistant acid phosphatase (TRAP) (P < 0.05), a bone resorption cytokine. Mice fed the HFs had 19.5% and 12.2% lower tibial and second lumbar vertebral bone mass, respectively (P < 0.01). Decreasing the dietary ratio of LA to ALA from 10 to 4 did not affect body mass, fat mass, serum TRAP and TNF-α, or any bone structural parameters. CONCLUSIONS: These data indicate that decreasing the dietary ratio of LA to ALA from 10 to 4 by simply reducing LA intake does not prevent adiposity or improve bone structure in obese mice.

Effect of Long-Term Green Tea Polyphenol Supplementation on Bone Architecture, Turnover, and Mechanical Properties in Middle-Aged Ovariectomized Rats.

We investigated the effects of 6-month green tea polyphenols (GTP) supplementation on bone architecture, turnover, and mechanical properties in middle-aged ovariectomized (OVX) rats. Female rats were sham-operated (n = 39, 13/group) or OVX (n = 143, 13/group). Sham-control and OVX-control rats (n = 39) receiving no GTP were assigned for sample collection at baseline, 3, or 6 months. The remaining OVX rats (n = 104) were randomized to 0.15%, 0.5%, 1%, and 1.5% (g/dL) GTP for 3 or 6 months. Blood and bone samples were collected. Relative to the OVX-control group, GTP (1% and 1.5%) lowered serum procollagen type 1 N-terminal propeptide at 3 and 6 months, C-terminal telopeptides of type I collagen at 3 months, and insulin-like growth factor-I at 6 months. GTP did not affect bone mineral content and density. At 6 months, no dose of GTP positively affected trabecular bone volume based on microCT, but a higher cortical thickness and improved biomechanical properties of the femur mid-diaphysis was observed in the 1.5% GTP-treated group. At 3 and 6 months, GTP (0.5%, 1%, and 1.5%) had lower rates of trabecular bone formation and resorption than the OVX-control group, but the inhibitory effects of GTP on periosteal and endocortical bone mineralization and formation at the tibial midshaft were only evident at 3 months. GTP at higher doses suppressed bone turnover in the trabecular and cortical bone of OVX rats and resulted in improved cortical bone structural and biomechanical properties, although it was not effective in preventing the ovariectomy-induced dramatic cancellous bone loss.

Depletion and repletion of fruit and vegetable intake alters serum bone turnover markers: a 28-week single-arm experimental feeding intervention.

This study was designed to evaluate the effects of elevated fruit and vegetable intake on bone turnover markers. In all, twenty-nine subjects (nine male and twenty female, with a mean age of 32·1 (sem 2·5) years) participated in a 28-week single-arm experimental feeding intervention trial and consumed a prescribed low-fruit and vegetable diet for 6 weeks (depletion-1), a provided high-fruit and vegetable diet for 8 weeks (fruit: 360-560 g; vegetables: 450-705 g), another prescribed low-fruit and vegetable diet for 6 weeks (depletion-2) and then their usual diets for 8 weeks (repletion). Serum bone-related biomarkers were analysed with commercial ELISA kits. Plasma carotenoid levels decreased as a result of the depletion phase and increased with the high-fruit and vegetable diet. Compared with the baseline, depletion-1 resulted in higher serum bone resorption marker C-terminal telopeptide of type 1 collagen (CTX) and lower bone formation marker alkaline phosphatase (BAP) (CTX, 0·68 (sem 0·05) v. 0·97 (sem 0·08) ng/ml and BAP, 10·7 (sem 0·7) v. 9·5 (sem 0·8) µg/l for the baseline and the depletion-1, respectively, P<0·05). High intake of fruit and vegetables decreased serum CTX (P<0·05) to 0·60 (sem 0·04) ng/ml and increased serum BAP to 11·3 (sem 0·7) µg/l (P<0·05), compared with the depletion-1 phase. Serum concentrations of CTX were inversely correlated and those of BAP were positively correlated with blood lycopene. These data show that increased fruit and vegetable consumption at or above federal dietary guidance may be beneficial to bone health.

A High-Fat Diet Decreases Bone Mass in Growing Mice with Systemic Chronic Inflammation Induced by Low-Dose, Slow-Release Lipopolysaccharide Pellets.

Background: Chronic inflammation is associated with increased bone resorption and is linked to osteopenia, or low bone mass. Obesity is also associated with low-grade chronic upregulation of inflammatory cytokines.Objective: This study investigated the effect of high-fat (HF) diet-induced obesity on bone structure changes in growing mice with existing systemic chronic inflammation induced by low-dose, slow-release lipopolysaccharide (LPS).Methods: Forty-eight 6-wk-old female C57BL/6 mice were randomly assigned to 4 treatment groups (n = 12/group) in a 2 × 2 factorial design-control (placebo) or LPS treatment (1.5 µg/d)-and consumed either a normal-fat (NF, 10% of energy as fat) or an HF (45% of energy as fat) diet ad libitum for 13 wk. Bone structure, serum biomarkers of bone turnover, and osteoclast differentiation were measured.Results: No alterations were observed in final body weights, fat mass, or lean mass in response to LPS treatment. LPS treatment increased serum concentration of tartrate-resistant acid phosphatase (TRAP, a bone resorption marker) and bone marrow osteoclast differentiation and decreased femoral and lumbar vertebral bone volume (BV):total volume (TV) by 25% and 24%, respectively, compared with the placebo. Mice fed the HF diet had greater body weight at the end of the study (P < 0.01) due to increased fat mass (P < 0.01) than did mice fed the NF diet. The HF diet increased serum TRAP concentration, bone marrow osteoclast differentiation, and expression of tumor necrosis factor α, interleukin 1ß and interleukin 6 in adipose tissue. Compared with the NF diet, the HF diet decreased BV:TV by 10% and 8% at femur and lumbar vertebrae, respectively, and the HF diet was detrimental to femoral and lumbar vertebral bone structure with decreased trabecular number and increased trabecular separation and structure model index.Conclusion: Results suggest that HF diets and systemic chronic inflammation have independent negative effects on bone structure in mice.

High Dietary Protein Intake and Protein-Related Acid Load on Bone Health.

PURPOSE OF REVIEW: Consumption of high-protein diets is increasingly popular due to the benefits of protein on preserving lean mass and controlling appetite and satiety. The paper is to review recent clinical research assessing dietary protein on calcium metabolism and bone health. RECENT FINDINGS: Epidemiological studies show that long-term, high-protein intake is positively associated with bone mineral density and reduced risk of bone fracture incidence. Short-term interventional studies demonstrate that a high-protein diet does not negatively affect calcium homeostasis. Existing evidence supports that the negative effects of the acid load of protein on urinary calcium excretion are offset by the beneficial skeletal effects of high-protein intake. Future research should focus on the role and the degree of contribution of other dietary and physiological factors, such as intake of fruits and vegetables, in reducing the acid load and further enhancing the anabolic effects of protein on the musculoskeletal system.

SHP2 regulates osteoclastogenesis by promoting preosteoclast fusion.

Genes that regulate osteoclast (OC) development and function in both physiologic and disease conditions remain incompletely understood. Shp2 (the Src homology-2 domain containing protein tyrosine phosphatase 2), a ubiquitously expressed cytoplasmic protein tyrosine phosphatase, is implicated in regulating M-CSF and receptor activator of nuclear factor-κB ligand (RANKL)-evoked signaling; its role in osteoclastogenesis and bone homeostasis, however, remains unknown. Using a tissue-specific gene knockout approach, we inactivated Shp2 expression in murine OCs. Shp2 mutant mice are phenotypically osteopetrotic, featuring a marked increase of bone volume (BV)/total volume (TV) (+42.8%), trabeculae number (Tb.N) (+84.1%), structure model index (+119%), and a decrease of trabecular thickness (Tb.Th) (-34.1%) and trabecular spacing (Tb.Sp) (-41.0%). Biochemical analyses demonstrate that Shp2 is required for RANKL-induced formation of giant multinucleated OCs by up-regulating the expression of nuclear factor of activated T cells, cytoplasmic 1 (Nfatc1), a master transcription factor that is indispensable for terminal OC differentiation. Shp2 deletion, however, has minimal effect on M-CSF-dependent survival and proliferation of OC precursors. Instead, its deficiency aborts the fusion of OC precursors and formation of multinucleated OCs and decreases bone matrix resorption. Moreover, pharmacological intervention of Shp2 is sufficient to prevent preosteoclast fusion in vitro. These findings uncover a novel mechanism through which Shp2 regulates osteoclastogenesis by promoting preosteoclast fusion. Shp2 or its signaling partners could potentially serve as pharmacological targets to regulate the population of OCs locally and/or systematically, and thus treat OC-related diseases, such as periprosthetic osteolysis and osteoporosis.

Smoke carcinogens cause bone loss through the aryl hydrocarbon receptor and induction of Cyp1 enzymes.

Smoking is a major risk factor for osteoporosis and fracture, but the mechanism through which smoke causes bone loss remains unclear. Here, we show that the smoke toxins benzo(a)pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) interact with the aryl hydrocarbon receptor (Ahr) to induce osteoclastic bone resorption through the activation of cytochrome P450 1a/1b (Cyp1) enzymes. BaP and TCDD enhanced osteoclast formation in bone marrow cell cultures and gavage with BaP stimulated bone resorption and osteoclastogenesis in vivo. The osteoclastogenesis triggered by BaP or RANK-L was reduced in Ahr(-/-) cells, consistent with the high bone mass noted in Ahr(-/-) male mice. The receptor activator of NF-κB ligand (RANK-L) also failed to induce the expression of Cyp1 enzymes in Ahr(-/-) cells. Furthermore, the osteoclastogenesis induced by TCDD was lower in Cyp1a1/1a2(-/-) and Cyp1a1/1a2/1b1(-/-) cultures, indicating that Ahr was upstream of the Cyp enzymes. Likewise, the pharmacological inhibition of the Cyp1 enzymes with tetramethylsilane or proadifen reduced osteoclastogenesis. Finally, deletion of the Cyp1a1, Cyp1a2, and Cyp1b1 in triple knockout mice resulted in reduced bone resorption and recapitulated the high bone mass phenotype of Ahr(-/-) mice. Overall, the data identify the Ahr and Cyp1 enzymes not only in the pathophysiology of smoke-induced osteoporosis, but also as potential targets for selective modulation by new therapeutics.

Role of glucocorticoid-induced leucine zipper (GILZ) in bone acquisition.

Glucocorticoids (GCs) have both anabolic and catabolic effects on bone. However, no GC anabolic effect mediator has been identified to date. Here we show that targeted expression of glucocorticoid-induced leucine zipper (GILZ), a GC anti-inflammatory effect mediator, enhances bone acquisition in mice. Transgenic mice, in which the expression of GILZ is under the control of a 3.6-kb rat type I collagen promoter, exhibited a high bone mass phenotype with significantly increased bone formation rate and osteoblast numbers. The increased osteoblast activity correlates with enhanced osteogenic differentiation and decreased adipogenic differentiation of bone marrow stromal cell cultures in vitro. In line with these changes, the mRNA levels of key osteogenic regulators (Runx2 and Osx) increased, and the level of adipogenic regulator peroxisome proliferator-activated receptor (PPAR) γ2 decreased significantly. We also found that GILZ physically interacts with C/EBPs and disrupts C/EBP-mediated PPARγ gene transcription. In conclusion, our results showed that GILZ is capable of increasing bone acquisition in vivo, and this action is mediated via a mechanism involving the inhibition of PPARγ gene transcription and shifting of bone marrow MSC/progenitor cell lineage commitment in favor of the osteoblast pathway.

Involuntary wheel running improves but does not fully reverse the deterioration of bone structure of obese rats despite decreasing adiposity.

This study investigated whether exercise or antioxidant supplementation with vitamin C and E during exercise affects bone structure and markers of bone metabolism in obese rat. Sprague-Dawley rats, 6-week old, were fed a normal-fat diet (NF, 10 % kcal as fat) and a high-fat diet (HF, 45 % with extra fat from lard) ad libitum for 14 weeks. Then, rats on the high-fat diet were assigned randomly to three treatment groups for additional 12 weeks with forced exercise: HF; HF + exercise (HF + Ex); and HF with vitamin C (0.5 g ascorbate/kg diet) and vitamin E (0.4 g α-tocopherol acetate/kg diet) supplementation + exercise (HF + Ex + VCE). At the end of the study, body weight and fat (%) were similar among NF, HF + Ex, and HF + Ex + VCE, whereas HF had greater body weight and fat (%) than other groups. Compared to NF, HF had elevated serum leptin, tartrate-resistant acid phosphatase (TRAP), and IGF-1; increased trabecular separation and structural model index; and lowered bone mineral density, trabecular connectivity density, and trabecular number in distal femur, while HF + Ex and HF + Ex + VCE had elevated serum TRAP and decreased bone volume/total volume and trabecular number of distal femurs. Compared to HF, HF + Ex and HF + Ex + VCE had decreased serum TRAP and osteocalcin and improved bone structural properties of the distal femur. These findings suggest that exercise, while decreasing body fat, does not fully protect against the negative skeletal effects of existing obesity induced by a high-fat diet. Furthermore, vitamin C and E supplementation has no additional benefits on bone structural properties during exercise.

Blocking antibody to the ß-subunit of FSH prevents bone loss by inhibiting bone resorption and stimulating bone synthesis.

Low estrogen levels undoubtedly underlie menopausal bone thinning. However, rapid and profuse bone loss begins 3 y before the last menstrual period, when serum estrogen is relatively normal. We have shown that the pituitary hormone FSH, the levels of which are high during late perimenopause, directly stimulates bone resorption by osteoclasts. Here, we generated and characterized a polyclonal antibody to a 13-amino-acid-long peptide sequence within the receptor-binding domain of the FSH ß-subunit. We show that the FSH antibody binds FSH specifically and blocks its action on osteoclast formation in vitro. When injected into ovariectomized mice, the FSH antibody attenuates bone loss significantly not only by inhibiting bone resorption, but also by stimulating bone formation, a yet uncharacterized action of FSH that we report herein. Mesenchymal cells isolated from mice treated with the FSH antibody show greater osteoblast precursor colony counts, similarly to mesenchymal cells isolated from FSH receptor (FSHR)(-/-) mice. This suggests that FSH negatively regulates osteoblast number. We confirm that this action is mediated by signaling-efficient FSHRs present on mesenchymal stem cells. Overall, the data prompt the future development of an FSH-blocking agent as a means of uncoupling bone formation and bone resorption to a therapeutic advantage in humans.

The central nervous system (CNS)-independent anti-bone-resorptive activity of muscle contraction and the underlying molecular and cellular signatures.

BACKGROUND: Mechanisms by which muscle regulates bone are poorly understood. RESULTS: Electrically stimulated muscle contraction reversed elevations in bone resorption and increased Wnt signaling in bone-derived cells after spinal cord transection. CONCLUSION: Muscle contraction reduced resorption of unloaded bone independently of the CNS, through mechanical effects and, potentially, nonmechanical signals (e.g. myokines). SIGNIFICANCE: The study provides new insights regarding muscle-bone interactions. Muscle and bone work as a functional unit. Cellular and molecular mechanisms underlying effects of muscle activity on bone mass are largely unknown. Spinal cord injury (SCI) causes muscle paralysis and extensive sublesional bone loss and disrupts neural connections between the central nervous system (CNS) and bone. Muscle contraction elicited by electrical stimulation (ES) of nerves partially protects against SCI-related bone loss. Thus, application of ES after SCI provides an opportunity to study the effects of muscle activity on bone and roles of the CNS in this interaction, as well as the underlying mechanisms. Using a rat model of SCI, the effects on bone of ES-induced muscle contraction were characterized. The SCI-mediated increase in serum C-terminal telopeptide of type I collagen (CTX) was completely reversed by ES. In ex vivo bone marrow cell cultures, SCI increased the number of osteoclasts and their expression of mRNA for several osteoclast differentiation markers, whereas ES significantly reduced these changes; SCI decreased osteoblast numbers, but increased expression in these cells of receptor activator of NF-κB ligand (RANKL) mRNA, whereas ES increased expression of osteoprotegerin (OPG) and the OPG/RANKL ratio. A microarray analysis revealed that ES partially reversed SCI-induced alterations in expression of genes involved in signaling through Wnt, FSH, parathyroid hormone (PTH), oxytocin, and calcineurin/nuclear factor of activated T-cells (NFAT) pathways. ES mitigated SCI-mediated increases in mRNA levels for the Wnt inhibitors DKK1, sFRP2, and sclerostin in ex vivo cultured osteoblasts. Our results demonstrate an anti-bone-resorptive activity of muscle contraction by ES that develops rapidly and is independent of the CNS. The pathways involved, particularly Wnt signaling, suggest future strategies to minimize bone loss after immobilization.

N-acetylcysteine supplementation decreases osteoclast differentiation and increases bone mass in mice fed a high-fat diet.

Obesity induced by high-fat (HF) diets increases bone resorption, decreases trabecular bone mass, and reduces bone strength in various animal models. This study investigated whether N-acetylcysteine (NAC), an antioxidant and a glutathione precursor, alters glutathione status and mitigates bone microstructure deterioration in mice fed an HF diet. Forty-eight 6-wk-old male C57BL/6 mice were randomly assigned to 4 treatment groups (n = 12 per group) and fed either a normal-fat [NF (10% energy as fat)] or an HF (45% energy as fat) diet ad libitum with or without NAC supplementation at 1 g/kg diet for 17 wk. Compared with the NF groups, mice in the HF groups had higher body weight, greater serum leptin concentrations and osteoclast differentiation, and lower trabecular bone volume, trabecular number, and connectivity density (P < 0.05). NAC supplementation increased the serum-reduced glutathione concentration and bone volume and decreased osteoclast differentiation in HF-fed mice (P < 0.05). We further demonstrated that osteoclast differentiation was directly regulated by glutathione status. NAC treatment of murine macrophage RAW 264.7 cells in vitro increased glutathione status and decreased osteoclast formation. These results show that NAC supplementation increases the bone mass of obese mice induced by an HF diet through elevating glutathione status and decreasing bone resorption.

Dietary protein level and source differentially affect bone metabolism, strength, and intestinal calcium transporter expression during ad libitum and food-restricted conditions in male rats.

High-protein (HP) diets may attenuate bone loss during energy restriction. The objective of the current study was to determine whether HP diets suppress bone turnover and improve bone quality in male rats during food restriction and whether dietary protein source affects this relation. Eighty 12-wk-old male Sprague Dawley rats were randomly assigned to consume 1 of 4 study diets under ad libitum (AL) control or restricted conditions [40% food restriction (FR)]: 1) 10% [normal-protein (NP)] milk protein; 2) 32% (HP) milk protein; 3) 10% (NP) soy protein; or 4) 32% (HP) soy protein. After 16 wk, markers of bone turnover, volumetric bone mineral density (vBMD), microarchitecture, strength, and expression of duodenal calcium channels were assessed. FR increased bone turnover and resulted in lower femoral trabecular bone volume (P < 0.05), higher cortical bone surface (P < 0.001), and reduced femur length (P < 0.01), bending moment (P < 0.05), and moment of inertia (P = 0.001) compared with AL. HP intake reduced bone turnover and tended to suppress parathyroid hormone (PTH) (P = 0.06) and increase trabecular vBMD (P < 0.05) compared with NP but did not affect bone strength. Compared with milk, soy suppressed PTH (P < 0.05) and increased cortical vBMD (P < 0.05) and calcium content of the femur (P < 0.01) but did not affect strength variables. During AL conditions, transient receptor potential cation channel, subfamily V, member 6 was higher for soy than milk (P < 0.05) and HP compared with NP (P < 0.05). These data demonstrate that both HP and soy diets suppress PTH, and HP attenuates bone turnover and increases vBMD regardless of FR, although these differences do not affect bone strength. The effects of HP and soy may be due in part to enhanced intestinal calcium transporter expression.

Soy protein isolates prevent loss of bone quantity associated with obesity in rats through regulation of insulin signaling in osteoblasts.

In both rodents and humans, excessive consumption of a typical Western diet high in saturated fats and cholesterol is known to result in disruption of energy metabolism and development of obesity and insulin resistance. However, how these high-fat, energy-dense diets affect bone development, morphology, and modeling is poorly understood. Here we show that male weanling rats fed a high-fat (HF) diet containing 45% fat and 0.5% cholesterol made with casein (HF-Cas) for 6 wk displayed a significant increase in bone marrow adiposity and insulin resistance. Substitution of casein with soy protein isolate (SPI) in the HF diet (HF-SPI) prevented these effects. Maintenance of bone quantity in the SPI-fed rats was associated with increased undercarboxylated osteocalcin secretion and altered JNK/IRS1/Akt insulin signaling in osteoblasts. The HF-Cas group had significantly greater serum nonesterified free fatty acid (NEFA) concentrations than controls, whereas the HF-SPI prevented this increase. In vitro treatment of osteoblasts or mesenchymal stromal ST2 cells with NEFAs significantly decreased insulin signaling. An isoflavone mixture similar to that found in serum of HF-SPI rats significantly increased in vitro osteoblast proliferation and blocked significantly reduced NEFA-induced insulin resistance. Finally, insulin/IGF1 was able to increase both osteoblast activity and differentiation in a set of in vitro studies. These results suggest that high-fat feeding may disrupt bone development and modeling; high concentrations of NEFAs and insulin resistance occurring with high fat intake are mediators of reduced osteoblast activity and differentiation; diets high in soy protein may help prevent high dietary fat-induced bone impairments; and the molecular mechanisms underlying the SPI-protective effects involve isoflavone-induced normalization of insulin signaling in bone.